In order to maintain the safety and reliability of devices at a nuclear power plant as well as the reactor internal components, each device and the reactor internal components are periodically inspected. Of these inspections, inspection of the reactor internal components is performed by indirect visual inspection by displaying a video image captured by an underwater TV camera or by a TV camera housed in a watertight case on a monitor at the inspection site, and having a skilled and experienced inspector visually check the video images on the monitor. Further, at a nuclear power plant, when work is performed to replace a device or a reactor internal component due to aged deterioration or damage, it is necessary to measure whether or not the position of the device after installation is correct.
However, since work to replace the device or the reactor internal component is performed using indirect visual observation and a target surface of relevant devices or the reactor internal components is checked using a video image that is displayed on a monitor, three-dimensional (3D) information cannot be obtained. When a pattern that appears to be a defect is present on the target surface of the device or the reactor internal components, it is difficult to judge whether the pattern is damage or a defect that has irregularities or is a pseudo pattern on the target surface, and a large amount of time and labor is required for this judgment.
Further, with respect to positional measurement after installation of a device or a reactor internal component of a nuclear power plant, a large amount of time and labor are required in order to measure the three-dimensional position of the devices or the reactor internal components based on a two-dimensional video image on a monitor.
In a conventional nuclear power plant, methods for acquiring three-dimensional information regarding the target surface of respective devices or the reactor internal components include the use of a stereoscopic apparatus that utilizes two cameras. Further, attempts are also being made to apply an inspection and measurement apparatus according to the principles of triangulation by using an optical measurement apparatus that utilizes one camera and a laser beam.
The conventional apparatus for inspecting and measuring has advantages and drawbacks with respect to dimensional measurement of an object to be measured or shape measurement of a device according to the state of the target surface of the respective devices or the reactor internal components that is the object to be measured. For example, with a stereoscopic apparatus that uses two cameras, it is necessary to correlate the positions at which the same location is imaged in images of two cameras. However, in the case of a target surface such as a metallic luster surface of an object to be measured, since there are no characteristic patterns on the surface it is not possible to appropriately determine a correspondence position among the camera images. Hence, it has been difficult to perform distance measurement such as for measuring the dimensions or shape of an object to be measured.
Further, according to the conventional apparatus for inspecting and measuring, a light section measuring method is available that utilizes a camera and line laser beams as an optical measurement apparatus. The optical measurement apparatus according to this method images with a camera a reflection of a line-shaped laser beam that is irradiated onto a target surface of an object to be measured, and measures irregularities in the target surface of the object to be measured based on a reflection position of the laser beam that appears in the camera image.
However, with a target surface that generates a secondary reflection of a laser beam such as a metallic luster surface of an object to be measured, there are cases in which an appropriate reflection position cannot be determined from a camera image, and distance measurement is therefore difficult. Further, since distance measurement is possible only at a position at which the laser beam is irradiated, there is the problem that it is necessary to minutely scan the laser beam in order to obtain high-density measurement points. Consequently, the measurement operation requires a large amount of time. Another representative measurement method of an optical measurement apparatus is a method in which a two-dimensional optical pattern is projected onto a target surface of an object to be measured, and the target surface onto which the optical pattern is projected is imaged with a camera.
According to this measurement method of an optical measurement apparatus, a known optical pattern that has been projected onto the target surface of the object to be measured is compared with the camera image, and irregularities on the target surface are measured based on a mapping position in the camera image of the optical pattern that is projected onto the target surface.
However, in some cases it is not possible to establish correspondence between an optical pattern projected onto a target surface of an object to be measured and a known optical pattern because the optical pattern is affected by the pattern of the target surface. Consequently, distance measurement is difficult since mapping positions cannot be obtained with the camera image.
Further, a common issue for conventional measurement apparatuses is that because the position of a camera or a laser beam or the like is fixed, it is necessary to keep a measurement distance between a measurement target and a measurement apparatus constant. Therefore in an environment in which a measurement apparatus is operated remotely, such as when inspecting a reactor internal component, there is the problem that, from an operability viewpoint, the measurement operation requires a large amount of time.